Bioactive oligopeptides

ABSTRACT

The invention relates to short 3- to 10-mer bioactive oligopeptides composed of amino acid residues selected from the group consisting of glycine, alanine, β-alanine, serine, histidine, glutamic acid, aspartic acid, lysine and arginine. They are able to improve at least one cell culture parameter such as growth rate, viable cell number, viability on day 6 or 7, or final product yield, when added to the basal nutrient medium. The invention further relates to mixtures of such oligopeptides and to a method of improving cell culture parameters by incubating animal or plant cells in the presence of said oligopeptides.

TECHNICAL FIELD

[0001] The invention relates to synthetic, short-chain oligopeptides with bioactive properties and their use for the supplementation of cell culture media.

BACKGROUND OF THE INVENTION

[0002] The biotechnological production of biologically active proteins is essential for the development of novel therapeutic and diagnostic tools and procedures. The majority of these synthetically produced peptides is at present obtained from animal cell cultures. In spite of rapidly accumulating knowledge in this field, some aspects of the in vitro production systems such as, for example, cell proliferation and cell death, are still not entirely controllable.

[0003] Industrial processes employing animal cells, particularly permanent animal cell lines, require cell numbers in the order of 10⁸ to 10¹² cells. According to GMP (good manufacturing practice), the production of a new lot of product has to be started by thawing a frozen cell stock from the master cell bank. The overall efficiency of the culturing and manufacturing process largely depends on the time period necessary for the first cycles of multiplication of the cells starting from a small frozen inoculum.

[0004] Speeding up the growth of the cell population can be achieved by supplementing the culture media with nutritional supplements or growth factors. For instance, it is known in the art to use glutamine dipeptide in replacement of monomeric glutamine, because the dimeric form of glutamine is more stable under cell culture conditions. Either way, however, glutamine as a monomer and as a dipeptide serves as a nutrient and is resorbed and matabolized by the cells of the cell culture.

[0005] Growth factors may be, for instance, components of animal sera. Their main disadvantage is that they are usually not well defined. Moreover, the use of components of direct animal origin is presently discouraged in pharmaceutical industry due to the danger of transferring viruses, prions or other possibly pathogenic agents from the animal body to the desired end product, e.g., the bioactive proteins. Alternatively, recombinant growth factors, such as insulin or members of the interleukin family, may serve as suitable growth stimulants. Another possibility is to use safe, chemically defined culture media free of any protein component. However, as a rule the generation time in protein-free media is longer than in media supplemented with serum.

[0006] Therefore, there is a great demand for techniques capable to intensify and accelerate the growth and/or product yield of cultured animal cells as well as the cell viability during incubation, particularly for industrial scale manufacturing processes. The present invention will contribute to satisfying this demand.

SUMMARY OF THE INVENTION

[0007] It has been found that small oligopeptides composed of a sequence of particular amino acid residues are capable of significantly promoting the cultivation of cells by enhancing the growth rate and/or the product yield or improve at least the maintainance (i.e. viability) of animal cell lines in culture when added to basal media containing otherwise suitable nutrient mixtures. Unlike the use of nutritional supplements such as, for instance, glutamine dipeptides, the present oligopeptides are not taken up by the cells in a substantial amount, i.e. not more than up to approximately 10% of the total amount of oligopeptides supplied to a cell culture medium is taken up by the cells and possibly metabolized. Experiments have shown that although a portion of the oligopeptides present in the nutrient medium may be hydrolyzed be exogenous proteases, neither the resulting monomers nor the remaining oligomers serve as nutritional factors.

[0008] Furthermore, when operating the cell cultures in a semi-continuous mode or in a fed-batch mode, i.e. by adding the required amino acids and, optionally, the oligopeptides of the present invention in intervals over the entire cultivation period of up to 8 days, the yield of the desired protein products obtainable from these animal cell cultures is augmented in addition to the biomass concentration, as shown in subsequent Tables 9 and 10.

[0009] The upper limit for the chain length of the amino acidsequence is primarily determined by the solubility of the respective peptides in the desired aqueous cell culture media. Usually, the chain length does not exceed six amino acid residues, because peptides longer than six amino acid residues cannot normally be dissolved at a concentration sufficiently high for effectively causing growth stimulation with the treated cells. In most cases, a chain length of three to five amino acid residues may be sufficient to produce the bioactive, e.g. growth stimulating, effects described herein.

[0010] The stimulatory effects on the cell cultures shows a tendency to increase with the oligopeptide concentration in the medium. In a preferred embodiment of the invention, oligopeptides or mixtures thereof are provided in a concentration range of 0.01 to 2.5 percent (w/v), i.e., 0.1 to 25 g/l, in particular from about 0.05 to 2% (w/v) corresponding to 0.5 to 20 g/l, in the cell culture nutrient medium, to effectively intensify the growth and/or product yield and the viability of the cultured cells.

[0011] The composition of the basal medium is not critical to the stimulatory effect of the present oligopeptides. Any suitable nutrient medium applicable in the cultivation of a desired animal cell line may be used. Also, the cell stimulating properties of the present oligopeptides are not restricted to any specific cell lines but apply to a multitude of different kinds of eukaryotic cells including plant and animal cells.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The terms “peptides” or “oligopeptides” as used herein relate to short peptides or amino acid sequences, preferably of synthetic origin, that consist of at least two amino acid residues, preferably L-a-amino acid residues, and that do not contain more than 10, preferably not more than six, amino acid residues.

[0013] It is to be understood that “incubation” or “cultivation” of cells is carried out ex vivo under conditons favouring cell growth and continued viability.

[0014] The term “bioactive” as used herein with regard to the activity of the present oligopeptides is meant to comprise at least one of the following acticities: cell growth stimulation, improvement of cell or cell culture viability (particularly at a time of incubation where cell viability starts to decline), increase of viable cell count, augmentation of product yield (e.g. of substances secreted by the cells, such as pharmaceutically active substances, drugs or antibodies), wherein this “bioactivity” of the oligopeptides is not due to a nutritional contribution of the oligopeptides. Indeed, the “bioactivity” of the present oligonucleotides is caused by effects other than a mere nutritional supplement or a compensation of nutritional deficiencies in a cell culture medium and has clearly been proven for complete nutrient media that are suitable for culturing a desired animal cell line in the absence of said oligopeptides.

[0015] The oligopeptides according to the present invention are preferably composed of amino acid residues derived from amino acids selected from the group consisting of glycine, alanine, β-alanine, serine, histidine, glutamic acid, aspartic acid, lysine and arginine. When added to a basal nutrient medium the oligopeptides are able to enhance at least one of the following cell culture parameters: number of viable cells, cell viability on day 6 or 7, viable cell count or the final product yield (e.g. a recombinant protein or an antibody). While the qualitative composition of the bioactive oligopeptides seems to be decisive for their stimulatory activity, it appears that the order of amino acids within the peptide chain may have less or no significance with regard to the extent of said activity.

[0016] Therefore, in one embodiment of the present invention the oligopeptide consists of two or more identical amino acid residues, preferably selected from the group consisting of glycine, alanine, β-alanine and serine.

[0017] In another embodiment, the oligopeptide comprises at least two, optionally three or more, identical amino acid residues selected from the group consisting of glycine, alanine, β-alanine and serine, threonine and, additionally, at least one amino acid residue selected from the group consisting of histidine, glutamic acid, aspartic acid, lysine and arginine.

[0018] The identical amino acid residues may be linked to each other either in a tandem arrangement or alternating with other residues within the oligopeptide.

[0019] Oligopetides which contain at least one amino acid residue of alanine and/or glycine, optionally in combination with at least one further amino acid residue, have found to be particularly useful for the cultivation of cells when added to the basal medium.

[0020] Examples of bioactive tripeptides used in the present invention include but are not limited to: Gly-Gly-Gly, Ser-Ser-Ser, Ala-Ala-Ala, βAla-βAla-βAla, Thr-Thr-Thr, Glu-Gly-Gly, Glu-Gly-Ala, Ala-Asp-Ala, Ala-His-Gly, Thr-Ala-Ser, Ser-Gly-Ala, Ala-Ala-Arg, βAta-Gly-Gly, Gly-Asp-Gly, Gly-His-Gly, Gly-Lys-Gly and Gly-Arg-Gly.

[0021] Examples of bioactive tetrapeptides used in the present invention include but are not limited to: Gly-Gly-Gly-Gly, Ala-Ala-Ala-Ala, βAla-βAla-βAla-βAla, Ser-Ser-Ser-Ser, Thr-Thr-Thr-Thr, Ser-Ser-Gly-Ala, Ser-Gly-Ser-Ala, Ala-His-Gly-Lys, Ser-Gly-Glu-Thr, Gly-Asp-Ala-Lys, Ala-Arg-Ser-Thr, Glu-Gly-Thr-His, βAla-βAla-βAla-Ser, Gly-Gly-His-Gly, Gly-Gly-Glu-Ala, Gly-Gly-Lys-Ala and Gly-βAla-Gly-Gly.

[0022] Examples of the pentapeptide used in the invention include but are not limited to: Gly-Gly-Gly-Gly-Gly, Ala-Ala-Ala-Ala-Ala, βAla-β-βAla-βAla-βAla, Ser-Ser-Ser-Ser-Ser, Thr-Thr-Thr-Thr-Thr, Ala-Ala-Ala-Gly-Ser, Ala-Ser-Ser-His-Thr, Gly-Ser-Gly-βAla-Gly, Gly-Thr-Arg-Ser-Ser, Ala-Ala-Gly-Gly-Lys, Glu-Ala-Ala-Ser-Ser. The cell cultures may be prepared and incubated according to methods well known in the art, e.g. using batch, fed-batch, semi-continuous or continuous operation modes. As during cultivation of the eukaryotic cells in the presence of the oligopeptides of the present invention the oligopetides are only slightly if at all metabolized there is usually no need for supplemental addition of the oligopeptides to the batch or fed-batch culture.

[0023] The bioactive properties of the present oligonucleotides also apply to plant cell cultures in a way very similar to the ones described herein for animal cells. Preliminary experiments (data not shown herein) have confirmed the beneficial utility of the oligopeptides for different plant cell cultures.

[0024] In order that the invention described herein may be more fully understood, the following examples are set forth. The examples are for illustrative purposes only and are not to be construed as limiting this invention in any respect.

EXAMPLE 1 Comparison of Changes in Amino Acid Concentration During the Cultivation Period of an Animal Cell Culture

[0025] Cells: Mouse hybridoma CAU 96 producing monoclonal IgG2a antibody. (Mouse hybridoma CAU 96 is a subclone, obtained through systemic adaptation to protein-free culture medium of hybridoma ME-750 (Franek F, Sramkova K (1998): in New Developments and New Applications in Animal Cell Culture Technology, pp 55-57, Dordrecht). The original hybridoma was constructed using the Sp2/O-Ag14 myeloma parent. This hybridoma produces an IgG2a monoclonal antibody reactive with an unidentified membrane antigen of pig lymphozytes. Hybridoma CAU 96 is deposited in the Institute of Experimaental Botany, Acadamy of Sciences of the Czech Republic, Prague.

[0026] Medium: DMEM/F-12/RPMI 1640 (2:1:1) supplemented with Basal Medium Eagle (BME) amino acids, 2.0 mM glutamine, 15 mM HEPES (N-2-Hydroxyethylpiperazine-N′-2-ethanesulfonic acid), 2.0 g/l sodium bicarbonate and 0.4 mM ferric citrate. (All medium components were obtained from Life Technologies)

[0027] Culture mode: 25 cm³ T-flasks (Nunc) culture volume 6.0 ml, placed at 37° C. in an incubator with 5% CO²; starting viable cell density is 3.1×10⁵ cells per ml.

[0028] Preparation of samples of amino acid analysis: Cells are removed by low-speed centrifugation and macromolecular components are removed by ultrafiltration. TABLE 1 Amino acid or Amino acid concentration, [mM] peptide Day 0 Day 4 Difference Lys 0.43 0.28 −0.15 His 0.18 0.14 −0.04 Arg 0.48 0.34 −0.14 Asp 0.06 0.02 −0.04 Thr + Asn 0.43 0.42 −0.01 Ser + Gln 2.94 0.91 −2.03 Glu 0.08 0.02 −0.06 Pro 0.37 0.49 +0.12 Gly 0.59 1.52 +0.93 Ala 0.73 2.02 +1.29 Val 0.72 0.56 −0.16 Met 0.24 0.17 −0.07 Ile 0.34 0.05 −0.29 Leu 0.08 0.04 −0.04 Tyr 0.45 0.41 −0.04 Phe 0.33 0.28 −0.05 Trp 0.05 0 −0.05 Tetraglycine 7.14 6.55 −0.59 Tetraglycine + Gly 7.73 8.06 +0.33

[0029] It appears, that the tetrameric glycine and alanine peptides are neither utilized nor metabolized by the cells as substrates for the synthesis of new cell mass, as shown in Table 1. The decrease of the oligoglycine, i.e. tetraglycine, concentration during the cultivation period is less than 10% (Table 1, penultimate line). Interestingly, the analytical data in Table 1 and Table 2 further suggest that the hydrolized fraction of tetraglycine or tetraalanine (probably hydrolyzed by peptidases released from the cells) is not consumed as a substrate. In the case of tetraglycine, the total glycine concentration, as well as the total sum of glycine and tetraglycine concentration (Table 1, ultimate line), is even higher after 4 days of culture than at the beginning. In the case of tetraalanine the total alanine concentration, as well as the sum of alanine and tetraalanine concentration increases during the cultivation period (Table 2, ultimate line). The decrease of tetraalanine concentration during the cultivation period corresponds to the increase of alanine concentration, most likely caused by hydrolysis of tetraalanine by peptidases released from the cells. TABLE 2 Amino acid or Amino acid concentration peptide Day 0 Day 4 Difference Lys 0.47 0.36 −0.11 His 0.18 0.12 −0.06 Arg 0.45 0.36 −0.09 Asp 0.10 0.05 −0.05 Thr + Asn 0.47 0.42 −0.05 Ser + Gln 2.38 0.85 −1.53 Glu 0.08 0.01 −0.07 Pro 0.39 0.43 +0.04 Gly 1.00 0.88 −0.12 Ala 0.48 2.68 +2.20 Val 0.47 0.35 −0.12 Met 0.18 0.11 −0.07 Ile 0.54 0.22 −0.32 Leu 0.55 0.22 −0.33 Tyr 0.25 0.11 −0.14 Phe 0.25 0.21 −0.04 Trp 0.05 0.01 −0.04 Tetraalanine 1.84 1.28 −0.56 Tetraalanine + Ala 2.32 3.86 +1.54

EXAMPLE 2 Effect of Varying Chain Length and Concentrations of Oligopeptides

[0030] Cells: Mouse hybridoma CAU 96 producing monoclonal IgG2a

[0031] Medium: DMEM/F-12/RPMI 1640 (2:1:1) supplemented with BME amino acids, MEM non essential amino acids, 2.0 mM glutamine, 15 mM HEPES, 2.0 g/L sodium bicarbonate and 0.4 mM ferric citrate.

[0032] Culture mode: 25 cm² T-flasks (Supplier: Nunc) with a culture volume of 6.0 ml, placed at 37° C. in an incubator with 5% CO₂

[0033] Starting viable cell density is 310000 (3.1*10⁵) cells per ml. TABLE 3 Effect of oligoglycines Day 7 Monoclonal Supplement (% in Viable cell number Viability antibody w/v) cells/μL % of control % mg/L None (Control) 1060 100 61 150 Glycine 0.2% 1080 102 60 160 Diglycine 0.2% 1210 114 70 165 Triglycine 0.2% 1660 157 75 160 Tetraglycine 0.2% 1870 176 80 170 Pentaglycine 0.2% 2020 190 82 165 Hexaglycine 0.2% 1940 183 79 160

[0034] Table 3 illustrates the effect of glycine oligopeptides of different chain length on the growth of the hybridoma cell line: the growth stimulating effect increases from diglycine to pentaglycine. The oligoglycine peptides act selectively on cell growth increasing both viable cell number and viability of the cells. The intensification of growth does not, however, automatically entail an increase in the yield of the desired protein product, e.g., an antibody. TABLE 4 Effect of oligoalanines Day 6 Monoclonal Supplement (% in Viable cell number Viability antibody w/v) cells/μL % of control % mg/L none (control) 1100 100 57 104 Alanine 0.2% 1030 94 60 110 Trialanine 0.2% 1420 129 70 132 Trialanine 0.1% 1390 126 69 130 Tetraalanine 0.2% 1560 142 72 153 Tetraalanine 0.1% 1370 125 66 133

[0035] Table 4 illustrates the effect of alanine and two oligoalanines differing in chain length on the growth of the hybridoma cell line. While the growth stimulating effect of alanine is insignificant, the stimulatory effect of oligoalanines is quite pronounced and increases from trialanine to tetraalanine. Both oligoalanines display higher growth-stimulating effect at 0.2% concentration than at 0.1% concentration. In the case of oligoalanines the intensification of growth is accompanied by an increase of the yield of the desired cell product, e.g. the monoclonal antibody. TABLE 5 Concentration-dependent effect of triserine, trithreonine and tri-β alanine Day 6 Monoclonal Viable cell number Viability antibody Supplement (% in w/v) cells/μL % of control % mg/L None (control) 1140 100 61 109 Serine 0.2% 1190 104 63 111 Triserine 0.3% 1610 141 78 142 Triserine 0.2% 1550 136 70 126 Triserine 0.1% 1340 118 65 112 Triserine 0.05% 1200 105 61 112 Threonine 0.2% 1100 97 59 114 Trithreonine 0.2% 1450 127 73 152 Trithreonine 0.1% 1370 120 70 130 Trithreonine 0.05% 1310 115 67 122 β-alanine 0.2% 1210 106 60 105 Tri-β-alanine 0.2% 1410 124 70 122 Tri-β-alanine 0.1% 1470 129 70 122 Tri-β-alanine 0.05% 1390 122 73 126 Tri-β-alanine 0.02% 1370 120 63 120 Tri-β-alanine 0.01% 1210 106 64 117

[0036] Table 5 illustrates that tripeptides composed of serine, threonine, or β-alanine are able to stimulate cell growth, while the effect of serine or β-alanine is insignificant. The effect of triserine and trithreonine on cell growth and antibody yield is highest at the highest peptide concentration tested, and decreases with concentration. Tri-p-alanine displays stimulating effect on cell growth and antibody yield at lower concentrations 0.1% (w/v) and 0.05% (w/v). TABLE 6 Effect of tripeptides consisting of two glycine residues and a residue of another amino acid Day 6 Monoclonal Supplement (% in Viable cell number Viability antibody w/v) cells/μL % of control % mg/L None (control) 1250 100 55 88 Gly-Gly-Gly 0.2% 1300 104 80 89 Gly-Gly-Gly 0.1% 1350 108 78 98 Gly-Asp-Gly 0.2% 1420 114 70 92 Gly-Asp-Gly 0.1% 1340 107 64 98 Gly-His-Gly 0.2% 900 72 66 144 Gly-His-Gly 0.1% 1180 94 65 121 Gly-Lys-Gly 0.2% 1100 88 62 154 Gly-Lys-Gly 0.1% 1250 100 67 128 Gly-Arg-Gly 0.2% 1270 102 66 121 Gly-Arg-Gly 0.1% 1360 109 65 106

[0037] Table 6 illustrates the effects of several tripeptides composed of glycine residues and residues of glutamic acid, aspartic acid, histidine, lysine or arginine. None of these peptides stimulates the cell growth in a significant manner. Higher concentrations (e.g. 0.2%) of peptides containing histidine or lysine suppress the growth of hybridoma cells. A common property of peptides containing histidine, lysine or arginine is a significant enhancement of antibody yield. All tripeptides tested improve the viability of the culture on day 6, i.e. at a time where viability of the cell culture starts to decline. The results demonstrate a 64 to 80% viability in the presence of the oligopeptides, compared to only 55% viability in the control without oligopeptides) TABLE 7 Effect of various tetrapeptides consisting of glycine, alanine, histidine, glutamic acid, lysine and β-alanine residues. Day 6 Viable cell number Monoclonal % of Viability antibody Supplement (% in w/v) cells/μL control % mg/L None (control) 1070 100 53 93 Gly-Gly-His-Gly 0.2% 1180 110 71 84 Gly-Gly-His-Gly 0.1% 1360 127 77 93 Gly-Gly-Glu-Ala 0.2% 1280 120 77 113 Gly-Gly-Glu-Ala 0.1% 1350 126 82 100 Gly-Gly-Lys-Ala 0.2% 1290 121 78 134 Gly-Gly-Lys-Ala 0.1% 1310 122 79 118 Gly-βAla-Gly-Gly 0.2% 1270 119 72 150 Gly-βAla-Gly-Gly 0.1% 1150 107 65 129 Gly-βAla-Gly-Gly 0.05% 1100 103 68 121

[0038] Table 7 illustrates that tetrapeptides consisting of glycine, β-alanine, glutamic acid, histidine and lysine are able to stimulate cell growth, at least at a concentration of 0.1 or 0.2%. While the enhancement of antibody yield due to the presence of the peptide containing histidine is insignificant, all other peptides increase the antibody yields. All tetrapeptides tested improve the culture viability on day 6 (65 to 82% viability with peptides versus 53% in the control without peptides)

EXAMPLE 3 Dependence of the Effect of Oligoglycine Peptides on the Concentrations Applied

[0039] Cells: Mouse hybridoma CAU 96 producing monoclonal IgG2a

[0040] Medium: DMEM/F-12/RPMI 1640 (2:1:1) supplemented with BME amino acids, MEM non essential amino acids, 2.0 mM glutamine, 15 mM HEPES, 2.0 g/L sodium bicarbonate and 0.4 mM ferric citrate.

[0041] Culture mode: 25 cm² T-flasks (Supplier: Nunc), culture volume 6.0 ml, placed at 37° C. in an incubator with 5% CO₂; starting viable cell density is 3.1×10⁵ cells per ml. TABLE 8 Day 7 Tetraglycine Monoclonal concentration Viable cell number Viability antibody % (w/v) cells/μL % of control % mg/L 0 1140 100 64 140 0.1 1750 154 78 125 0.2 2220 195 77 120 0.3 2370 208 80 110

[0042] From Table 3 it is derivable that glycine monomer does not significantly stimulate cell growth, while from dimeric to pentameric glycine an increasingly stimulating effect is noted. Table 8 illustrates for tetraglycine how the concentration of oligopetides in the cell culture medium affects cell growth. Indeed, cell density and viability is improved already at a tetraglycine concentration as low as 0.1%. On the other hand, the monoclonal antibody yield slightly decreases with increasing tetraglycine concentration and increasing viable cell number. This effect may possibly be similar to a certain extent to the well known distinction between growth phase and metabolite production and/or excretion phase in many conventional microbiological fermentation processes.

EXAMPLE 4 Steady State in Semi-Continuous Culture in the Presence of Tetraglycine

[0043] Cells: Mouse hybridoma CAU 96 producing monoclonal IgG2a

[0044] Medium: DMEM/F-12/RPMI 1640 (2:1:1) supplemented with BME amino acids, MEM non essential amino acids, 2.0 mM glutamine, 15 mM HEPES, 2.0 g/L sodium bicarbonate and 0.4 mM ferric citrate.

[0045] Culture mode: Semicontinuous culture in 25 cm² T-flasks, total volume 6 ml, placed at 37° C. in an incubator with 5% CO₂; starting viable cell density is 3.1×10⁵ cells per ml. A volume of 2.0 ml culture is withdrawn every day and replaced by 2.0 ml fresh medium (including the oligopeptides for the experimental cell culture, but without olipeptides for the control culture).

[0046] In semi-continuous culture both the viable cell density and viability, as well as the monoclonal antibody concentration are positively influenced by tetraglycine (see Table 9). TABLE 9 Viable cell number Viability Monoclonal Antibody Medium cells/μL % mg/L Mean ± S.D. Standard medium 1740 ± 80 83 ± 2 43 ± 6 (control) Standard medium + 0.2% 2240 ± 20 91 ± 2 52 ± 8 tetraglycine

EXAMPLE 5 Comparison of Batch and Fed Batch Mode Culture

[0047] Cells: Mouse hybridoma CAU 96 producing monoclonal IgG2a.

[0048] Medium: DMEM/F-12/RPMI 1640 (2:1:1) supplemented with BME amino acids, MEM non essential amino acids, 2.0 mM glutamine, 15 mM HEPES, 2.0 g/L sodium bicarbonate and 0.4 mM ferric citrate.

[0049] Culture mode: 25 cm² T-flasks (Nunc), culture volume 6.0 ml, placed at 37° C. in an incubator with 5% CO₂; starting viable cell density is 3.1×10⁵ cells per ml.

[0050] Batch: without feeding.

[0051] Fed batch: 0.2 ml concentrated BME amino acid solution added daily from day 1. TABLE 10 Standard medium (control) Medium + 0.2% (w/v) tetraglycine Viable cell Monoci. Viable cell number Monoci. number Viability antibody % of Viability antibody Day cells/μL % mg/L cells/μL control % mg/L BATCH 0 280 88 9 280 100 89 9 4 1640 89 n.d. 2070 138 89 n.d. 8 990 49 71 1660 168 58 69 FED BATCH 0 280 88 9 280 100 88 9 4 1850 90 n.d. 2940 159 81 n.d. 8 1720 60 143 2150 125 49 189

[0052] Feeding a concentrated amino acid solution to the starting medium results in a significant increase in the yield of the final product, e.g., the monoclonal antibodies. While in simple batch mode culture the addition of tetraglycine does not influence the final product yield, in the fed batch culture the positive effects of feeding and intensified cell growth resulted in an additive enhancement of the final product yield.

EXAMPLE 6 Effect of Tetraglycine on the Growth of CHO Cells

[0053] Cells: CHO dhf

[0054] Basal medium: DMEM/F12 supplemented with BME amino acid mixture and

[0055] MEM non-essential amino acid mixture, 0.5 mM ferric citrate

[0056] Culture mode: Batch culture in 25 cm² T-flasks (Nunc), culture volume 6.0 ml, placed at 37° C. in an incubator with 5% CO₂.

[0057] Starting viable cell density: 180000 cells per ml TABLE 11 Viable cell number, day 6 Supplement cells per μL % of control None (control) 440 100 Tetraglycine, 1.25% 530 120 Tetraglycine, 2.5% 810 184

[0058] Tetraglycine also significantly affects the growth of CHO cells, suggesting that it may have a non-species specific growth stimulating effect on a variety of animal cells.

Example 7 Combination of Various Tetrapeptides

[0059] Cells: Mouse hybridoma CAU 96 producing monoclonal IgG2a antibody

[0060] Medium: DMEM/F-12/RPMI 1640 (2:1:1) supplemented with BME amino acids, MEM non essential amino acids, 2.0 mM glutamine, 15 mM HEPES, 2.0 g/L sodium bicarbonate and 0.4 mM ferric citrate.

[0061] Culture mode: 25 cm² T-flasks (Nunc) with a culture volume of 6.0 ml, placed at 37° C. in an incubator with 5% CO₂.

[0062] Starting viable cell density is 310000 (3.1*10⁵) cells per ml TABLE 12 Day 6 Viable cell number Monoclonal % of Viability antibody Supplement (% in w/v) cells/μL control % mg/L None (control) 1100 100 58 96 Gly-Gly-His-Gly 0.1 % 1570 143 67 68 Gly-Gly-Glu-Ala 0.1 % Gly-Gly-His-Gly 0.1% + 1650 150 71 98 Gly-βAla-Gly-Gly 0.1% Gly-Gly-His-Gly 0.1% + 1420 129 73 110 Gly-Gly-Lys-Ala 0.1% Gly-Gly-Glu-Ala 0.1% + 1200 109 69 94 Gly-Gly-Lys-Ala 0.1 Gly-Gly-Lys-Ala 0.1% + 1470 134 77 111 Gly-βAla-Gly-Gly 0.1% Gly-Gly-Glu-Ala 0.1% + 1430 130 69 74 Gly-βAla-Gly-Gly 0.1%

[0063] Table 12 demonstrates that tetrapeptides comprising amino acid residues selected from the group consisting of glycine, alanine, histidine, glutamic acid, lysine and β-alanine residues stimulate cell growth when added as a combination of two different peptides. The growth promoting activity of the oligopeptide pairs does not likewise extend, however, to the product, i.e. antibody yield. On the contrary, the product yield is lower than in case of application of the corresponding single tetrapeptides, as referred to in Table 7. All of the peptide pairs retain their ability of improving the culture viability on day 6.

1 29 1 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 1 Gly Gly Gly Gly 1 2 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 2 Ala Ala Ala Ala 1 3 4 PRT Artificial Sequence PEPTIDE (1)..(4) /note Xaa = bAla 3 Xaa Xaa Xaa Xaa 1 4 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 4 Ser Ser Ser Ser 1 5 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 5 Thr Thr Thr Thr 1 6 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 6 Ser Ser Gly Ala 1 7 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 7 Ser Gly Ser Ala 1 8 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 8 Ala His Gly Lys 1 9 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 9 Ser Gly Glu Thr 1 10 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 10 Gly Asp Ala Lys 1 11 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 11 Ala Arg Ser Thr 1 12 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 12 Glu Gly Thr His 1 13 4 PRT Artificial Sequence PEPTIDE (1)..(3) /note Xaa = bAla 13 Xaa Xaa Xaa Ser 1 14 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 14 Gly Gly His Gly 1 15 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 15 Gly Gly Glu Ala 1 16 4 PRT Artificial Sequence Description of Artificial Sequence linear peptide 16 Gly Gly Lys Ala 1 17 4 PRT Artificial Sequence PEPTIDE (2) /note Xaa = bAla 17 Gly Xaa Gly Gly 1 18 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 18 Gly Gly Gly Gly Gly 1 5 19 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 19 Ala Ala Ala Ala Ala 1 5 20 5 PRT Artificial Sequence PEPTIDE (1)..(5) /note Xaa = bAla 20 Xaa Xaa Xaa Xaa Xaa 1 5 21 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 21 Ser Ser Ser Ser Ser 1 5 22 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 22 Thr Thr Thr Thr Thr 1 5 23 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 23 Ala Ala Ala Gly Ser 1 5 24 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 24 Ala Ser Ser His Thr 1 5 25 5 PRT Artificial Sequence PEPTIDE (4) /note Xaa = bAla 25 Gly Ser Gly Xaa Gly 1 5 26 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 26 Gly Thr Arg Ser Ser 1 5 27 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 27 Ala Ala Gly Gly Lys 1 5 28 5 PRT Artificial Sequence Description of Artificial Sequence linear peptide 28 Glu Ala Ala Ser Ser 1 5 29 6 PRT Artificial Sequence Description of Artificial Sequence linear peptide 29 Gly Gly Gly Gly Gly Gly 1 5 

What is claimed is:
 1. Use of a bioactive oligopeptide consisting of 2-10, preferably 3-6, amino acid residues, for increasing the yield of a desired cell product in an animal or plant cell culture, as compared to a control without said oligopeptide, substantially without said oligopeptide being utilized as a source of nutrition by the cells of the cell culture.
 2. (new) Use of a bioactive oligopeptide consisting of 2-10, preferably 3-6, amino acid residues, for the manufacture of a cell culture nutrient medium for increasing the yield of a desired cell product in an animal or plant cell culture, as compared to a control without said oligopeptide, substantially without said oligopeptide being utilized as a source of nutrition by the cells of the cell culture.
 3. (new) Use of a bioactive oligopeptide consisting of 2-10, preferably 3-6, amino acid residues, for supplementing a basal nutrient medium suitable for animal or plant cell culture, for increasing the yield of a desired cell product in an animal or plant cell culture, as compared to a control without said oligopeptide, substantially without said oligopeptide being utilized as a source of nutrition by the cells of the cell culture.
 4. (new) Use according to any one of claims 1 to 3, comprising an oligopeptide having at least two identical amino acid residues, preferably selected from the group consisting of glycine, alanine, P-alanine, serine and threonine residues.
 5. (new) Use according to any one of claims 1 to 4, comprising an oligopeptide having three to six identical amino acid residues.
 6. (new) Use according to any one of claims 1 to 5, comprising an oligopeptide of which at least one amino acid residue is selected from the group consisting of histidine, glutamic acid, aspartic acid, lysine and arginine residues.
 7. (new) Use according to any one of claims 1 to 6, comprising an oligopeptide having at least two identical amino acid residues selected from the group consisting of glycine, alanine, β-alanine, serine, and threonine residues and, additionally, at least one amino acid residue selected from the group consisting of histidine, glutamic acid, aspartic acid, lysine and arginine residues.
 8. (new) Use according to any one of claims 4 to 7, comprising an oligopeptide wherein identical amino acid residues are arranged in a tandem arrangement.
 9. (new) Use according to any one of claims 1 to 8, comprising a mixture of different oligopeptides, optionally having different chain lengths.
 10. (new) Use according to any one of claims 1 to 9, wherein the oligopeptides are selected from the group consisting of Ser-Ser-Ser, Ala-Ala-Ala, βAla-βAla-βAla, Gly-Gly-Gly, Thr-Thr-Thr, Gly-His-Gly, Gly-Lys-Gly, Gly-Arg-Gly, Gly-Gly-Gly-Gly (SEQ ID NO:1), Ala-Ala-Ala-Ala (SEQ ID NO:2), βAla-βAla-βAla-βAla (SEQ ID NO:3), Gly-Gly-Glu-Ala (SEQ ID NO: 15), Gly-Gly-Lys-Ala (SEQ ID NO:16), Gly-βAla-Gly-Gly (SEQ ID NO:17), Gly-Gly-Gly-Gly-Gly (SEQ ID NO:18), Ala-Ala-Ala-Ala-Ala (SEQ ID NO: 19), βAla-βAla-βAla-βAla-βAla (SEQ ID NO:20), Gly-Gly-Gly-Gly-Gly-Gly (SEQ ID NO:29).
 11. (new) Use according to any one of claims 1 to 10, wherein the oligopeptides are used at a concentration of 0.01 to 2.5 percent (w/v), corresponding to 0.1 to 25 g per liter cell culture nutrient medium.
 12. (new) Use according to any one of claims 1 to 11, wherein the desired cell product is a pharmaceutically active substance, preferably a drug or an antibody, optionally secreted by the cells.
 13. (new) A nutrient medium suitable for animal or plant cell culture, comprising a bioactive oligopeptide capable of increasing the yield of a desired cell product in an animal or plant cell culture, as compared to a control without said oligopeptide, substantially without said oligopeptide being utilized as a source of nutrition by the cells of the cell culture, which oligopeptide consists of 3 to 10, preferably 3 to 6, amino acid residues, and has at least two identical amino acid residues, preferably selected from the group consisting of glycine, alanine, β-alanine, serine and threonine residues, and wherein said oligopeptide is neither tri- nor tetraglycine.
 14. (new) The nutrient medium according to claim 13, comprising a bioactive oligopeptide that has three to six identical amino acid residues.
 15. (new) The nutrient medium according to claim 13 or 14, comprising a bioactive oligopeptide which contains at least one amino acid residue selected from the group consisting of histidine, glutamic acid, aspartic acid, lysine and arginine residues.
 16. (new) The nutrient medium according to any one of claims 13 to 15, comprising a bioactive oligopeptide that has at least two identical amino acid residues selected from the group consisting of glycine, alanine, β-alanine, serine, and threonine residues and, additionally, at least one amino acid residue selected from the group consisting of histidine, glutamic acid, aspartic acid, lysine and arginine residues.
 17. (new) The nutrient medium according to any one of claims 13 to 16, comprising a bioactive oligopeptide wherein identical amino acid residues are arranged in a tandem arrangement.
 18. (new) The nutrient medium according to any one of claims 13 to 17, comprising a bioactive oligopeptide selected from the group consisting of Ser-Ser-Ser, Ala-Ala-Ala, βAla-βAla-βAla, Thr-Thr-Thr, Gly-His-Gly, Gly-Lys-Gly, Gly-Arg-Gly, Ala-Ala-Ala-Ala (SEQ ID NO:2), βAla-βAla-βAla-βAla (SEQ ID NO:3), Gly-Gly-Glu-Ala (SEQ ID NO:15), Gly-Gly-Lys-Ala (SEQ ID NO:16), Gly-βAla-Gly-Gly (SEQ ID NO: 17), Gly-Gly-Gly-Gly-Gly (SEQ ID NO: 18), Ala-Ala-Ala-Ala-Ala (SEQ ID NO:19), βAla-βAla-βAla-βAla-βAla (SEQ ID NO:20), and Gly-Gly-Gly-Gly-Gly-Gly (SEQ ID NO:29).
 19. (new) A nutrient medium according to any one of claims 13 to 18, comprising bioactive oligopeptides in a concentration of 0.01 to 2.5% (w/v), corresponding to 0.1 to 25 g per liter, preferably in a concentration of 0.1 to 0.5% (w/v), corresponding to 1 to 5 g per liter.
 20. (new) A bioactive oligopeptide capable of increasing the yield of a desired cell product in an animal or plant cell culture, as compared to a control without said oligopeptide, substantially without said oligopeptide being utilized as a source of nutrition by the cells of the cell culture, which oligopeptide consists of 3 to 10, preferably 3 to 6, amino acid residues, and has has at least two identical amino acid residues selected from the group consisting of glycine, alanine, β-alanine, serine, and threonine residues and, additionally, at least one amino acid residue selected from the group consisting of histidine, glutamic acid, aspartic acid, lysine and arginine residues, and wherein said oligopeptide is neither tri- nor tetraglycine.
 21. (new) The bioactive oligopeptide according to claim 20, selected from the group consisting of Ser-Ser-Ser, Ala-Ala-Ala, βAla-βAla-βAla, Thr-Thr-Thr, Gly-His-Gly, Gly-Lys-Gly, Gly-Arg-Gly, Ala-Ala-Ala-Ala (SEQ ID NO:2), βAla-βAla-βAla-βAla (SEQ ID NO:3), Gly-Gly-Glu-Ala (SEQ ID NO:15), Gly-Gly-Lys-Ala (SEQ ID NO:16), Gly-βAla-Gly-Gly (SEQ ID NO:17), Gly-Gly-Gly-Gly-Gly (SEQ ID NO:18), Ala-Ala-Ala-Ala-Ala (SEQ ID NO:19), βAla-βAla-βAla-βAla-βAla (SEQ ID NO:20), and Gly-Gly-Gly-Gly-Gly-Gly (SEQ ID NO:29). 